1. Field of the Invention
The present invention relates to an all-solid-state cell utilizing a combination of an electrode active substance and a solid electrolyte.
2. Description of the Related Art
In recent years, with the advancement of portable devices such as personal computers and mobile phones, there has been rapidly increasing demand for batteries usable as a power source thereof. In cells of the batteries for the purposes, a liquid electrolyte (an electrolytic solution) containing a combustible organic diluent solvent has been used as an ion transfer medium. The cell using such an electrolytic solution can cause problems of solution leakage, ignition, explosion, etc.
In view of solving the problems, all-solid-state cells, which use a solid electrolyte instead of the liquid electrolyte and contain only solid components to ensure intrinsic safety, have been developing. The all-solid-state cell contains a sintered ceramic as the solid electrolyte, and thereby does not cause the problems of ignition and liquid leakage, and is hardly deteriorated in battery performance by corrosion. Particularly all-solid-state lithium secondary cells can achieve a high energy density easily, and thus have been actively studied in various fields (see, for example, Japanese Laid-Open Patent Publication Nos. 2000-311710 and 2005-063958, Yusuke Fukushima and four others, “Fabrication of electrode-electrolyte interface in all-solid-state lithium batteries using the thermal softening-adhesion behavior of Li2S—P2S5 glass electrolytes”, Lecture Summary of Chemical Battery Material Association Meeting, Vol. 9th, Pages 51-52, issued on Jun. 11, 2007).
Japanese Laid-Open Patent Publication No. 2005-063958 discloses a thin-film, solid, lithium ion secondary cell. The secondary cell described in Japanese Laid-Open Patent Publication No. 2005-063958 is a bendable thin-film cell having a flexible solid electrolyte and thin layers of positive and negative electrode active substances sputtered thereon. The electrodes of the cell have to be thin, and the amounts of the electrode active substances are limited. Thus, the cell is disadvantageous in that it is difficult to achieve a high capacity.
The article of Fukushima et al. reports formation of an electrode-electrolyte interface of a complex of a glass electrolyte and an electrode active substance, utilizing softening fusion of the glass electrolyte. In this report, it is described that the resistance between electrolyte particles is effectively lowered due to the fusion of the glass electrolyte, and further a heterophase is not formed in a reaction between the electrolyte material and the active substance material.
However, an all-solid-state cell having positive and negative electrodes is not described in this report, and it is unclear whether the reaction resistance can be lowered in the electrolyte-electrode active substance interface. Further the relation between the electric properties and the fact that the heterophase is not formed is not specifically described, and the charge-discharge ability of the all-solid-state cell is unknown. Furthermore, the electrolyte used in this report is a sulfide, which is expected to be unstable in the atmosphere (air). The electrolyte may generate a toxic gas when brought into contact with the air due to breakage or the like. Thus, this technology is disadvantageous in unestablished safety.